As is already known, the secondary of a typical ignition coil produces a very high voltage, such as to enable an electrical arc to be generated across the electrodes of the sparking plugs, thus igniting the fuel/air mixture contained in the cylinders in the engine block.
Commonly, one single coil controls all of the spark plugs via, for example, a mechanical distributor, generally of the kind having a rotating distributor arm. Such an installation has the drawback that it necessitates a bundle of high tension cables which connect the secondary of the ignition coil to the distributor, and the distributor to each of the spark plugs. Apart from the cost of this bundle of cables, the latter is subject to electrical losses, which give rise to parasitic radio-electric waves; this is quite acceptable when a mechanical distributor is used, but such waves interfere very significantly with the ignition system when this latter is of the kind that includes electronic modules in place of a mechanical distributor.
In order to overcome the above disadvantages, it has already been proposed to associate on ignition coil individually with each spark plug. The present invention is particularly applicable to such a coil (referred to here as a "single cylinder ignition coil") which includes a closed-circuit magnetic assembly comprising a central magnetic core, around which two spools of plastics material are arranged coaxially. The primary and secondary windings are wound on these spools, and the assembly so formed is integrated into a housing which is formed by moulding over it in plastics material. A synthetic resin is flowed into the interior of the housing so as to encapsulate the various components of the ignition coil and to insulate them electrically from each other.
One of the problems to be overcome in an ignition coil of this type is that of how to construct a high tension connecting means which is such as to enable the electrical connection between the end of the secondary winding and the corresponding spark plug to be achieved, and in particular the connection between the end of the secondary winding and the high tension output member which makes direct contact with the spark plug associated with the coil.
This output member commonly consists of a carbon brush which is held in contact with the end of the spark plug through a spring. Such a carbon brush is inevitably subject to wear and embrittlement, due in particular to the high temperatures to which it is subjected. In addition, its retention in its housing calls for more or less complex solutions which considerably add to the cost of the ignition coil.